1. Field of the Invention
This invention relates to polycarbonate or polyestercarbonate resins.
2. Description of Prior Arts
Recently, transparent resins being excellent in various characteristics are required as materials for shaped articles in a wide variety of fields such as optical devices and automobile parts. In particular, in optical recording media such as optical disks and optical memory cards, new systems where users can record information have appeared, such as write-once system and re-writable system, and with development of such recording systems the level of requirement for various characteristics of substrate materials have been enhancing. Three characteristics are particularly required, namely low water absorption (small warping caused by water absorption), low birefringence and high thermal resistance. Glass and plastics are currently used as materials for the substrates. Since glass substrates have drawbacks of low mass-productivity, being expensive and heavy, and breaking readily, plastic materials, which do not have the drawbacks of glass, are mainly used for the substrates. Also for other optical elements, e.g. lenses such as concave/convex lenses and Fresnel lens, diffraction gratings, etc., plastic materials are going to be the main stream for the same reasons as those in the case of optical recording media.
Poly(methyl methacrylate) (hereinafter referred to as PMMA) and bisphenol A polycarbonate (hereinafter referred to as PC) are currently used as the transparent optical materials. Although PMMA has very low birefringence, it has drawbacks of having high water (moisture) absorption property and warping or deforming by water absorption, resulting in a decrease in its optical characteristics. In particular, when PMMA is used as the material for optical recording media composed of a single substrate, such as digital audio disks, accurate reproduction of the recorded signals is often impossible. Furthermore, optical recording media comprising FMMA as the substrate material have some problem in thermal resistance. On the other hand, PC has low water absorption property, warps only little and has no problem in thermal resistance, but it has a serious drawback that its birefringence is large. The birefringence of digital audio disks or small-diameter lenses can be suppressed within the required level under extremely careful molding conditions. However, the large-size optical elements such as laser-vision disks having a diameter of 30 cm or large-diameter lenses with the minimized birefringence cannot be produced even under such extremely careful molding conditions.
It has been reported that the glass transition temperatures of polyesters having norbornane skeleton, perhydrodimethanonaphthalene skeleton and perhydrotrimethanoanthracene skeleton are higher in the order listed, and that they are higher than those of polyesters having no such skeletons [cf. Journal of Polymer Science: Polymer Chemistry Edition, 10, p.3191 (1972)]. It is also known that the polyesters having the above-mentioned skeletons are excellent in dimensional stability and are used as supports for photographic elements (cf. U.S. Defensive Publication No. 896,033).
An object of the present invention is to provide a novel polycarbonate or polyestercarbonate resin having excellent transparency and thermal resistance, and having little warp or deformation caused by water absorption.
Another object of the present invention is to provide a novel polycarbonate or polyestercarbonate resin having excellent transparency, thermal resistance and resistance to high temperature and high humidity, and having little warp or deformation caused by water absorption.
Still another object of the present invention is to provide a novel polycarbonate or polyestercarbonate resin having a high glass transition temperature and thermal resistance, being little sensitive to birefringence, having excellent transparency, and having little warp or deformation caused by water absorption.
These objects as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description.